Last week, Financial Times Chief Foreign Affairs Correspondent Gideon Rachman did me the honor of linking my name with the illustrious historians Paul Kennedy (Yale University) and Niall Ferguson (Harvard University). For an academic, there are few greater professional pleasures than being compared with scholars whose work you admire. But as Rachman went on to say in his column, the reason he lumped me in with Kennedy and Ferguson was not to puff up my ego; it was to point out that the three of us compose a "triumvirate of declinist Brits."

The theme of Rachman's piece came from Britain's recent decision to join the new Beijing-based Asian Infrastructure Investment Bank, despite American objections. This move, Rachman suggested, was merely a symptom of growing British doubts about America's global leadership. He argued that the declinist triumvirate has contributed to these doubts because "it often falls to British academics based in America to play the role of insider-outsider, commenting on the decline of today’s pre-eminent global power, the US.” Rachman went on to suggest that "it is possible that British professors based in America have the right combination of knowledge and detachment to have an unclouded vision of America’s future. Alternatively, it is also possible that they may be over-projecting the fate of the British Empire.”

Rachman's column cuts to the heart of the issue I have raised in each of my columns: What can strategic forecasters learn from history?

Choosing the Best Analogy

In my opening salvo back in January, I suggested that the first step to answering this question is to distinguish between formal and relational analogies. Formal analogies compare similarities between a well-understood case, such as the British Empire, and a less-understood case, such as today's American hegemony. Then, on the basis of those similarities, logicians predict other ways in which the second case might be like the first, too.

By contrast, relational analogies focus on broad patterns linking numerous cases. Logicians can then look not only for general trends that could show us where current events are heading, but also for differences between examples that could indicate the case being analyzed might diverge dramatically from the general path. Though a formal analogy between today's global order and the British Empire of the 19th century is certainly easier to make than a relational analogy between the current order and all previous international systems, it is also highly vulnerable to the over-projection of a single case that Rachman condemns.

But if instead we look at America's dominance in the context of the 5,000-year history of state systems, rather than just comparing it with the British Empire, we begin to see a glaring regularity: Every earlier empire, or alliance, or whatever term we want to use for the current U.S. system, eventually declined and fell, without exception. As George Friedman pointed out in his most recent Geopolitical Weekly, U.S. hegemony may be the strongest the world has ever seen, but it is still bound by the same limits as its predecessors.

This doesn't mean America's decline is certain. History has also showed us that nothing is inevitable. Some things, though, are very close, and the historical pattern of the rise and fall of empires points toward two broad conclusions. First, we should demand very strong evidence indeed before concluding that America will defy the trends that have bound everyone else for the last five millennia. Second, until someone produces such evidence, the important question seems not to be whether U.S. dominance will decline, but rather when and under what circumstances. Once we reframe the question this way, Rachman's triumvirate of declinist Brits immediately breaks down, because Kennedy, Ferguson and I see different patterns in the past, with different implications for the future.

Three Interpretations of History

In his 1987 classic, The Rise and Fall of the Great Powers, Kennedy argued that all great Western powers since A.D. 1500 were drawn into increasingly extensive strategic entanglements that forced them to spend more of their GDP on defense, contributing to domestic underinvestment. The result of this cycle was always the same: As the great power sunk into relative economic decline, its rivals became emboldened and challenged it more often, bankrupting the great power with many great wars. Eventually, a new great power rose to replace the old.

When Kennedy's book was published, some readers were tempted to reduce his relational analogy to a formal one, casting the contemporary United States in the role of Britain in 1910, just as its primacy was about to unravel. But this was overly simplistic, because it overlooked the differences between the American and British cases — differences that brought an American boom rather than bust in the 1990s, and a Soviet collapse rather than an American one in the face of Kennedy's law of imperial overstretch. These victories did not mean that the United States had refuted the trend of empires; only that it had lived to fight another day.

A year after Kennedy's book came out, archaeologist Joseph Tainter offered a very different account of the fall of empires in The Collapse of Complex Societies. Looking back to Rome, Tainter suggested that the loss of confidence within the imperial elite has brought empires down. In his recent books, Empire and Civilization, Ferguson identified the same force at work in both early 20th-century Britain and early 21st-century America. He observes that by the 1920s, men like George Orwell, Harry St. John Bridger Philby (the father of the spy Kim Philby) and E.M. Forster — men who, in Victorian times, may well have devoted their lives to serving the empire — had walked away from their posts with disgust for the entire enterprise. Ferguson sees a similar pattern among American elite in the 2010s, concluding that, "maybe the real threat is posed not by the rise of China, Islam or CO2 emissions, but by our own loss of faith in the civilization we inherited from our ancestors."

My own interpretation of what history tells us about America's future is different. In Why the West Rules — For Now and War! What Is It Good For?, I look back across the past 20,000 years, and what strikes me most is the interplay between geography and social development. In the 16th and 17th centuries, rising levels of development enabled Western Europeans to transform the Atlantic Ocean from a barrier to movement to a superhighway. In the 19th century, the control of this superhighway made Britain the world's first global power. But as development rose faster still, geography's meaning continued to change. By the early 20th century, the United States had pushed the United Kingdom from the top of the heap, and by the early 21st century, the Pacific Ocean had become the world's new superhighway, driving up East Asian development and enabling China to challenge America for global dominance.

As I see it, we should expect the United States to remain an indispensable nation for another generation, perhaps even two, but probably not three. But the rise of the East is not the only dynamic we need to consider when projecting future power structures. As social development rises ever higher, revolutions in genetics, computing, robotics and nanotechnology are beginning to feed back into our biology, transforming what it means to be human. As these changes accelerate, old-fashioned debates about whether America is number one may become increasingly irrelevant.

The Right Lesson

This is why Rachman is simultaneously right, wrong and missing the point when he talks about a "triumvirate of declinist Brits." While I would like to believe that being a British professor in the United States gives me an unclouded vision of America's future, none of the wildly varying predictions that we triumvirs have produced has much to do at all with our status as "insider-outsiders." After all, the thoroughly American Robert D. Kaplan is as “declinist” as any Brit, arguing in Asia's Cauldron that "the age of simple American dominance … will likely have to pass. A more anxious, complicated world awaits us."

Comparing these different predictions suggests to me that strategic forecasters can learn two things from history. First, while no one can accurately predict the future, we can sometimes get a sense of the probabilities of different outcomes. (It is possible that American hegemony, like the Kingdom of Heaven, will be eternal, but it probably will not.) Second, forecasters profit most from history not when they ask experts for the answer to a question, but when they recognize the disagreements among experts and engage with the reasons behind them. Perhaps American dominance will collapse in the 2010s, eaten away by self-doubt, or perhaps it will last for another six or seven decades, steering the world through revolutionary upheavals. By thinking about the flaws of historians' conclusions, policymakers will truly learn from the past.

The day before Rachman's column came out, former U.S. Treasury Secretary Larry Summers blogged about Britain's decision to join the Asian Infrastructure Investment Bank. Summers, however, stressed the options open to America. "What is crucial," he said, "is that the events of the past month will be seen by future historians not as the end of an era, but as a salutary wake-up call."

That, I would say, is the right lesson to learn from history.

Ian Morris is a historian and archaeologist. He is currently Stanford University's Jean and Rebecca Willard Professor of Classics and serves on the faculty of the Stanford Archaeology Center. He has published twelve books and has directed excavations in Greece and Italy. Dr. Morris' bestsellers include Why the West Rules -- for Now (2010) and War! What Is It Good For? Conflict and the Progress of Civilization from Primates to Robots (2014). His most recent book is Foragers, Farmers, and Fossil Fuels: How Human Values Evolve, released in 2015 by Princeton University Press. He received his doctorate from Cambridge University.